Investigations on a hybrid chemo-magnetorheological finishing process for freeform surface quality enhancement

Surface roughness improvement of the freeform surfaces is essential for the enhanced functionality of the components, including implants, turbine blades, microchannels, etc. The exclusion of human involvement during the finishing of freeform surfaces prevents hazardous exposure to particulate and provides uniform surface quality. Different surface finishing techniques, including vibratory finishing, Abrasive Flow Finishing (AFF), Electron Beam (EB) Irradiation, Electrolytic in-process Dressing (ELID) grinding, etc., have been developed to automate the finishing operation. However, some limitations are associated with the preexisting techniques, e.g., the process controllability of AFF and vibratory finishing, recast layer formation during EB irradiation, and low productivity of ELID grinding. Hence, a novel method for surface improvement, namely, Hybrid Chemo-Magnetorheological Finishing (HC-MRF), is proposed in the present study to reduce the surface roughness (R-a) (similar to up to a few nanometer) without affecting the surface topography of the workpiece. HC-MRF simultaneously utilizes the synergic action between Magnetorheological Finishing (MRF) and chemical etching to reduce surface finishing time and escalate process efficiency. Herein, the carrier medium of the Magnetorheological (MR) fluid is replaced by a reagent to facilitate the chemical etching process, and its synchronized action with mechanical abrasion reduces surface irregularities. Furthermore, the design of the developed apparatus to enable the HC-MRF process, where permanent magnets are used to produce the desired external magnetic field, is also discoursed. A case study on the surface roughness enhancement through the HC-MRF on the WC-Co (tungsten carbide in a cobalt-rich matrix) is investigated using Response Surface Methodology (RSM). Herein, Murakami's reagent is used as the carrier medium in the MR fluid, and a reduction in surface roughness (R-a) from an initial value of 312.87 nm to a final value of 34.50 nm is noticed. Moreover, the inclusion of Murakami's reagent enhances the process efficiency. The change in surface roughness with and without Murakami's reagent in the MR fluid is 88.97 % and 43.12 %, respectively, for a constant finishing time.